There are guidelines and draft international standards regarding the measurement of industrial robots.
Such guidelines include the "VDI-Richtlinion VDI 3861" "KenngroBen fur Handhabungsgerate" Sheet 1 (1980), "KenngroBen fur Industrieroboter, Einsatzspexifische KenngroBen" Sheet 2 (1987) and "KenngroBen fur Industrieroboter, Prufung der KenngroBen" Sheet 3 (1987) issued by Verein Deutscher Ingenieure.
There is also a Draft International Standard ISO/DIS 9283 "Manipulating industrial robots--performance criteria and related test methods", issued by the International Organization for Standardization (1988).
Publications by Bernhard Reichling; "Roboter auf dem Prufstand" in "Roboter" March 1986, pp. 22-24 (1986) and "Lasergestutzte Positions- und Bahnvermessung von Industrierobotern" Thesis, Universitat Karlsruhe (1988) describe a measuring system for robots. This measuring system is based on a conventional interferometer. The measuring system is capable of measuring in six degrees of freedom. The measuring system consists of a fixed interferometer and a carrier mounted on the tool center point. There is a laser beam of the interferometer. A second beam is emitted by a semiconductor laser diode parallel to the interferometer laser beam. The carrier contains an optical system, which projects both laser beams on three position sensitive detectors. All angles of orientation can be determined unambiguously from the signals provided by the position sensitive detectors. In combination with the interferometer, the deviation of the movement of the robot from a reference trajectory can be measured in six degrees of freedom.
A laser tracking system measuring more than three degrees of freedom is described in a paper by Kam Lau, Robert Hocken and Leonard Haynes "Robot Performance Measurements using Automatic Laser Tracking Techniques" in "Robotics and Computer-Integrated Manufacturing" Vol. 2 No. 3/4 pp. 227-236 (1985). A laser beam is deflected by a cardanically mounted first mirror. A plane second mirror is mounted on the end-effector of a robot. This second mirror can be rotated about two axes. The mirror is rotated by a servo system to be always perpendicular to the laser beam. The distance between the two mirrors is measured interferometrically.
These two systems require active elements on the end-effector of the robot. Such elements add weight to the end-effector. There is also the problem of transmitting signals to and from the end-effector.
A thesis by S. Decker "Dynamisches externes RoboterbahnmeBsystem--Ein Beitrag zur Bestimmung dynamischer KenngroBen von Industrierobotern" Technische Universitat Wien, describes a laser tracking system which permits the tracking of the three degrees of freedom of position. A robot carries, at its tool center point, a retro-reflector. The laser beam of an interferometer is deflected by a mirror to this retro-reflector. The mirror can be rotated about two axes to track the retro-reflector. The laser beam is returned by the retro-reflector to the mirror and to the interferometer. The parallel displacement between the incident and returned beam is proportional to the distance of the incident beam from the center point of the reflector. This displacement is measured by means of a position sensitive detector, onto which part of the returned beam is deflected by a semi-transparent mirror. The signal of the position sensitive detector is the error signal of a control device which rotates the mirror so as to minimize the displacement between incident and returned beam. Thereby the deflected laser beam is caused to follow arbitrary movements of the retro-reflector. The laser beam "tracks" the retro-reflector. Using the distance between mirror and retro-reflector as provided by the interferometer and the angles of rotation of the mirror provided by two high-precision angular encoders, the three-dimensional position of the retro-reflector in an instrument-fixed reference coordinate system is computed.
This prior art laser tracking system provides only the position of the retro-reflector and, thereby, of the end-effector of the robot but does not provide the orientation of the retro-reflector.